There are four valves in the heart that serve to direct blood flow through the two sides of the heart. One of these valves is the aortic valve, which is located between the left ventricle and the aorta. The aortic valve plays a vital role in helping to direct oxygenated blood from the lungs through the left side of the heart and into the aorta for distribution to the body. Like the other major heart valves, the aortic valve is a passive structure in that it does not expend any energy in opening and closing. More specifically, the aortic valve has three leaflets that open and close in response to differential pressures on either side of the aortic valve. The aortic valve, along with the pulmonary valve, is referred to as a “semi-lunar valve” because of its unique appearance of its leaflets, which are shaped somewhat like a half-moon and are sometimes called “cusps”. The aortic valve, along with the pulmonary valve, has three cusps.
Heart valves, including the aortic valve, can exhibit abnormal anatomy and function as a result of congenital or acquired valve disease. Congenital valve abnormalities may be well tolerated for many years only to develop a life-threatening problem in an elderly patient, or may be so severe that emergency surgery is required within the first few hours of life. Acquired valve disease may result from causes such as rheumatic fever, degenerative disorders of the valve tissue, bacterial or fungal infections, and trauma.
Since the aortic valve is a passive structure that simply opens and closes in response to differential pressures on either side of the valve, the problems that can develop can be classified into two categories: (1) stenosis, in which the aortic valve does not open properly, and (2) insufficiency (also called regurgitation), in which the aortic valve does not close properly. Stenosis and insufficiency can occur concomitantly. Both of these abnormalities increase the workload placed on the heart. The severity of this increased stress on the heart and the patient, and the heart's ability to adapt to it, determine whether an abnormal aortic valve or its individual leaflets have to be surgically replaced, most often by replacing the entire valve with an artificial valve such as an artificial mechanical valve or an artificial tissue valve.
On information and belief, the currently available replacement options cannot duplicate the advantages of native (natural) heart valves. Some of the available mechanical valves tend to be very durable, but are problematic in that they are thrombogenic and exhibit relatively poor hemodynamic properties. In addition, mechanical valve replacements tend to replace in total all three leaflets of the aortic valve including undamaged and adequately performing aortic leaflets or cusps. Some of the available artificial tissue valves may have relatively low thrombogenicity, but often do not exhibit hemodynamic properties that approach the advantageous hemodynamic performance of a native valve. Thus, there is a need for an apparatus and method for more specific replacement of aortic leaflets, which also offers the flexibility of replacing individual leaflets.
A description of the prior art follows.
U.S. Publication No. 20020077698, published Jun. 20, 2002 (issued May 6, 2003 as U.S. Pat. No. 6,558,417) to Peredo, describes a semi-lunar stentless valve formed entirely of biological tissue. The Peredo valve has a plurality of leaflets that are joined to form an annulus and coapt to form a one-way valve. The leaflets are described as having the capability to open fully to minimize obstruction. A narrow rim of tissue is provided over commissures where the leaflets join around a base of the valve for a serving ring. According to the Peredo '698 patent publication, the valves can be sutured to heart tissue wall in a single suture row.
U.S. Pat. No. 6,328,763, issued to Love et al., describes a method of reconstructing a three-dimensional semi-lunar heart valve, or portion thereof based on optimized geometry of a tissue pattern for semi-lunar heart valve reconstruction. In one described embodiment, the two-dimensional valve tissue pattern comprises a two-dimensional configuration developed and optimized by employing, in part, the anatomy of a three-dimensional human heart valve, and the two-dimensional configuration delimits a two dimensional area that corresponds to the shape of tissue to be used in the repair of at least one leaflet of a circulatory system semi-lunar valve, wherein the configuration delimits at least one segment, and up to all three segments, of a three segment “trefoil” shape.
Geometric optimization of a tissue pattern for semi-lunar valve reconstruction was also described in an article published in November, 1999 (Hanlon J G, Suggit R W, Gibbs E, McMeeking R M, Love J W, J Heart Valve Dis., November 1999; 8(6): 609-13). The methodology included computer-assisted design (CAD) to create an optimized leaflet geometry based on published dimensions for normal human aortic valves. In contrast, the Applicant's invention as claimed takes into account the actual dimensions of the aortic valve or aortic leaflets.
Pericardium tissue proved useful in repairing heart valves, but such materials were often attacked by the patient's immune system. Medical workers such as Love suggested using autologous pericardium, treated with a brief immersion in a glutaraldehyde (GA) solution, for use in an autologous tissue replacement for heart valves (Love et al., “Rapid intraoperative fabrication of an autogenous tissue heart valve: A new technique,” Proceedings of the Third International Symposium on Cardiac Bioprostheses 691-698 (1986)). Later, Love reported that glutaraldehyde treated autologous pericardium, does not thicken or shrink, is resistant to calcific degeneration, and is durable beyond 25 equivalent years in the accelerated life tester. (Love et al., “Experimental evaluation of an autologous tissue heart valve. Journal of Heart Valve Disease,” 1992; 1232-241). However, while antigenicity issues were reduced using glutaraldehyde treated pericardium and hemodynamic (blood flow) properties were improved over mechanical valve replacements, the optimum design of aortic leaflets has remained an issue. The terms “GA” and “glutaraldehyde” are hereinafter regarded as equivalent terms.
U.S. Pat. No. 6,726,715, issued Apr. 27, 2004 to Sutherland, describes a heart valve prosthesis for use as an aortic or pulmonary replacement valve, or as a mitral or tricuspid valve. The '715 heart valve includes leaflets that are reinforced with oriented fiber components in a laminated composite, in which the fiber-reinforcing materials are oriented to match lines of stress to provide a long-lived valve that provides strength at points of maximal stress that have hitherto been foci for material failure. In a preferred embodiment involving a stentless valve, the reinforcing materials are described as optimized in terms of the density and orientation of the fibers in the composite materials to extend the life of a stentless valve.
U.S. Publication No. 20040138743, published Jul. 15, 2004 to Myers et al., describes a tubular prosthetic semi-lunar or atrioventricular heart valve that is said to be formed by cutting flat, flexible leaflets according to a pattern. The valve is constructed by aligning the side edges of adjacent leaflets so that the leaflet inner faces engage each other, and suturing the leaflets together with successive stitches along a fold line adjacent the side edges. The stitches are placed successively from a proximal in-flow end of each leaflet toward a distal out-flow end. During operation, when the leaflets open and close, the leaflets fold along the fold line. Distal tabs extend beyond the distal end of each leaflet. The successive stitches terminate proximal of the distal tab portion so that no locked stitches are placed along the distal portion of the fold line. The tab portions of adjacent leaflets are folded over each other and sewn together to form commissural attachment tabs. The commissural tabs provide commissural attachment points to accommodate sutures and the like in order to secure the tab to a vessel wall, if a semi-lunar valve, and papillary muscles and/or chordae tendineae if an atrioventricular valve.
U.S. Pat. No. 6,837,902, issued Jan. 4, 2005 to Nguyen et al., describes heart valve leaflet selection methods and apparatuses which subject individual leaflets to loads and measure the resulting deflection to more reliably group leaflets of similar physical characteristics for later assembly in prosthetic heart valves. The deflection testing may be accomplished using a variety of test set ups that are designed to impart a load on the leaflet, which simulates the actual loading within a heart valve. The results from a number of deflection tests are used to categorize individual leaflets, which data can be combined with other data regarding the characteristics of the leaflet to better select leaflets for assembly into a multi-leaflet heart valve. In one embodiment, the deflection test is combined with an intrinsic load test, and leaflets having similar deflection and intrinsic load values used in the same heart valve. One apparatus for testing the leaflets includes a frame for securing the arcuate cusp of the leaflet while the straight coapting edge remains free, to simulate the actual leaflet mounting configuration within the heart valve prosthesis. The frame may include a lower portion having a recess for the leaflet and plurality of receptor holes around the peripheral edge of the recess, and an upper portion having a plurality of needles, which extend downward through the leaflet and into the receptor holes and secure the edges of the leaflet.
U.S. Pat. No. 6,613,087, issued Sep. 2, 2003 to Healy et al., describes a prosthetic stentless aortic tissue valve includes a substantially annular valve body having a leaflet carried therein for occluding blood flow therethrough. A root extends generally coaxially from the valve body. Visual marking are provided on the root and act as a sculpting guide for a surgeon during implantation of the prosthetic heart valve to sculpt portions of sinus areas of the root.
U.S. Pat. No. 6,613,086, issued Sep. 2, 2003 to Moe et al., describes a tri-leaflet prosthetic cardiac valve with leaflets having an analytic shape in a selected position. The leaflets are connected to a valve body at attachment curves. The shape of the leaflet is selected from a set of geometries that can be represented mathematically. The attachment curve is selected to improve the durability of the tri-leaflet valve by moving the point of maximum loaded stress along the attachment curve away from the commissures. An inner wall of the valve body is given a non-circular shape near the attachment curve, the shape of the inner wall corresponding to the attachment curve. Also, a method of making a valve by selecting an analytic leaflet shape, selecting an attachment curve to improve durability of the valve by moving the point of maximum loaded stress along the attachment curve away from the commissures, and forming a valve body to support one or more leaflets, the valve body having a non-circular inner wall conforming to the attachment curve.
U.S. Pat. No. 6,491,511, issued Dec. 10, 2002 to Duran et al., describes a pair of templates that form a mold for substantially flat biological membranes to shape the membrane into a configuration that, after trimming of excess tissue, is adapted for forming a replacement aortic, pulmonary, tricuspid or mitral heart valve. Each template has three members joined to another laterally, with each member configured to form, together with its mating member, the mold for one leaflet or cusp of the replacement heart valve. The negative template has concave surfaces for each member and the positive template has convex surfaces that mate with the concave surfaces of the first template. Each of the templates is made of thin, shell like material and has beveled edges. The biological membrane is placed between the mating convex and concave surfaces of the two templates assembled to one another to form the membrane into the configuration of the three leaflets of the replacement heart valve.
U.S. Pat. No. 6,113,631, issued Sep. 5, 2000 to Jansen, describes a mitral valve prosthesis that consists of a support housing (stent) with a base ring that bears at least two stays which substantially extend in the ring axis direction and are connected by curved wall for securing two flexible cusps. In order to obtain as uniform and reduced forces as possible between the cusps and the support housing, the connection lines between the cusps and the top inner edge of the wall lie each in a plane.
U.S. Pat. No. 5,713,953, issued Feb. 3, 1998 to Vallana et al., describes a stentless prosthesis that is made completely from material, for example bovine pericardium, other than valve material. A projection of the valve sleeve allows reparatory operations on surrounding tissues.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.